Retreaded tires provide an economical way to gain additional use from tire casings after the original tread or retread has become worn. According to a conventional method of retreading, sometimes referred to as cold process retreading, worn tire tread on a used tire is removed to create a buffed, generally smooth treadless surface about the circumference of the tire casing to which a new layer of tread may be bonded. After the worn tire tread is removed, the tire casing is typically inspected for injuries, some of which may be skived and filled with a repair gum while others may be severe enough to warrant rejection of the casing.
After completion of the skiving process, the buffed surface may be sprayed with a tire cement that provides a tacky surface for application of bonding material and new tread. Next, a layer of cushion gum may be applied to the back, i.e., the inside surface of a new layer of tread, or alternatively, the layer of cushion gum may be applied directly to the tacky surface on the tire casing. Conventionally, the cushion gum is a layer of uncured rubber material. The cushion gum and new tread may be applied in combination about the circumference of the tire casing to create a retreaded tire assembly for curing. The cushion gum may form the bond between the tread and the tire casing during curing. Following assembly of the tire casing, cement, cushion gum and tread, the overall retreaded tire assembly may be placed within a flexible rubber envelope. The entire envelope tire assembly may be placed within a curing chamber and subjected to a vulcanization process that binds the materials together.
Several different methods may be used to perform the inspection of the used tire casing prior to application of the new tread. One method may be a visual inspection. A visual inspection typically involves an inspector visually observing the tire casing as it rotates on a test stand. While a visual inspection may be useful for detecting large flaws in used tire casings, many tire defects, such as small or obscure holes, are difficult to detect in a visual inspection. Moreover, visual inspections can be slow and time consuming. If flaws are overlooked during the inspection, it may lead to a defective retreaded tire.
Other tire inspection methods involve the use of a testing head or probe that carries a high voltage. The probe is applied to the interior surfaces of a tire being tested while a corresponding grounding element, which may be part of a tire spreader or tire rotating device, is applied to the outside of the tire opposite the probe. Defects are detected by arcing between the testing head and the grounding element through the defect.
With such testing devices, the probe is generally supported on the end of a mechanical arm that can be used to help manipulate the probe between the beads of the tire casing and into the interior of the tire casing. However, the mechanical arms used to move the probes can still make it difficult to maneuver the probe into the proper position inside the tire casing. In many cases, despite the use of the adjustable arm, operator intervention may be required to help the probe pass between the beads of the tire casing and into the interior of the tire casing. This can make the inspection process more time consuming and increase the chance that the probe is positioned incorrectly in the tire casing. Additionally, many mechanical arms used with high voltage testing probes are not easily adapted to different sized and/or configured tires. As a result, a large number of different mechanical arms may be necessary for different tire sizes or the mechanical arm may require a large number of adjustments to accommodate tires of different sizes. In either case, it results in a more time consuming and cumbersome inspection process.